This is a proposal for a broad-based study of binaural hearing. The goal is to develop an integrated understanding of the processing of sound by the two ears, and to apply this understanding to improving the functional hearing abilities of people with hearing impairments or neurological disorders. This program contains extensive interplay between psychophysical studies and theoretical modeling. The proposed work incorporates theoretical studies of both physiological and psychophysical phenomena for both normal and abnormal auditory systems. -Proposed experimental studies include psychophysical studies of listeners with normal hearing as well as psychophysical studies of subjects with hearing losses or neurological disorders. Since it is a primary goal to investigate the relation of psychophysical performance to physiological mechanisms, considerable work is proposed to develop quantitative models of the processing of neural patterns by brainstem neurons that are sensitive to binaural stimulation and to incorporate descriptions of the physiological activity of these neurons into models of the psychophysical abilities of normal and impaired listeners. Measurements on impaired listeners include headphone and free-field measurements and will test classical psychophysical abilities as well as the processing of complex sound fields. Binaural hearing tests will be developed to isolate the specific difficulties of impaired listeners, and signal processing schemes will be recommended to minimize. the impact of these difficulties for listening in complex (noisy and reverberant) environments.